This invention relates to a method for recovering actinide elements from acidic radioactive waste solutions resulting from the reprocessing of irradiated nuclear reactor fuel.
One of the major problems confronting the nuclear power industry is management of the highly radioactive liquid wastes which result from the reprocessing of irradiated nuclear reactor fuel. One approach is to solidify the liquid wastes as they come from the reprocessing facility into a stable solid material which can be stored in the earth for a period of time sufficient for the radiation to decay to safe levels. However, the storage times required to achieve safe levels of radioactivity are on the order of a million years. This is far longer than the geological stability of the earth can be expected to be maintained. One solution is to remove the extremely long-lived radioactive components from the waste solutions--such as the actinides, i.e. the uranium, americium, curium, plutonium and neptunium--so that the remaining radioactive elements, presenting the bulk of the radioactive waste, need only be stored for up to 1000 years before the radioactivity reaches background levels. This time period is within the realm of determining geological integrity. The actinides thus recovered from the waste can then be reprocessed and recycled to provide additional fuel for nuclear power reactors and for isotopic power sources.
One major problem with recovering the actinides from large volumes of acidic high-level radioactive waste solutions is to find a method which will do so effectively and economically, since the actinides are present in several valence states and difficult to recover together. The extractant, di-hexoxyethylphosphoric acid, (hereinafter HDHoEP) is known to extract tetra and hexavalent actinides from an acidic solution, along with some fission products and rare earths. However, because the extractant has a strong affinity for the actinide elements, there has heretofore been no effective means for recovering or backextracting the actinides from the HDHoEP extractant and for separating the actinides from the co-extracted elements.